1. Technical Field
The present disclosure relates to semiconductor devices, and particularly relates to power transistors used in inverters, power conditioners, and power supply circuits.
2. Description of the Related Art
Recently, field effect transistors (FET) including gallium nitride (GaN) semiconductors as high-frequency high-power devices have been actively developed. GaN can form a variety of mixed crystals with aluminum nitride (AlN) and indium nitride (InN).
In particular, in hetero junctions of nitride semiconductors, a high concentration of two-dimensional electron gas (2DEG) is generated at the junction interface by spontaneous polarization or piezoelectric polarization without doping. Field effect transistors and Shottky barrier diodes (SBDs) including such 2DEG-rich layers as carriers have been receiving attention as high-frequency and high-power devices.
This novel material GaN has many problems related to its reliability, particularly low moisture resistance. As a method of improving moisture resistance, a technique of disposing a metallic layer including one of Ti, Ta, and Pt over openings formed in a protective film disposed over electrode pads to block a path of water invasion is disclosed (see Japanese Unexamined Patent Application Publication No. 2010-15370).